Data mining and decision support technologies use machine learning to identify patterns in data sets. Machine learning techniques include data classification, data clustering, pattern recognition, and information retrieval. Technology areas that utilize machine learning include merchandise mark-down services in retail applications, clinician diagnosis and treatment plan assistance based on similar patients' characteristics, and general purpose data mining. The various machine learning techniques rely, at their most basic level, on a distance between pairs of data points in a set of data as a measure of similarity or dissimilarity. Machine learning has become one of the most popular data analysis and decision making support tool in recent years. A wide variety of data analysis software packages incorporate machine learning to discover patterns in large quantities of data.